1. Field of the Invention
The present invention relates to telecommunications and, more particularly, to a method and system for effecting a vertical handoff that is requested by a user of a mobile node.
2. Description of Related Art
There is an increased interest in providing wireless telecommunications systems that support high data rates. One such approach is a “data-only” approach, often referred to as “EV-DO,” in which communications over the air interface are in the form of data packets, whether the underlying media being transferred is voice, data, or some other type. The EV-DO approach makes use of an “IS-856” air interface protocol that is described in a number of specifications. For example, Revision A of the IS-856 protocol is described in 3rd Generation Partnership Project 2, “cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-A, v1.0 (March 2004), which is incorporated herein by reference. This air interface protocol can provide peak data rates as high as 3.1 Mbps on the forward link and 1.8 Mbps on the reverse link. In contrast, “legacy” air interface protocols, such as IS-2000, typically provide much lower data rates.
Although high data rate protocols, such as IS-856, provide many advantages over legacy protocols, such as IS-2000, the processing of upgrading to IS-856 may occur over an extended period of time and/or may occur in only certain areas. Thus, a mobile node roaming through a wireless service provider's network may encounter some areas in which both IS-856 and IS-2000 coverage is available but may also encounter certain areas in which only IS-2000 coverage is available.
To address the use of different air interface protocols in different areas, many mobile nodes are able to communicate using multiple air interface protocols. Thus, a mobile node may be able to communicate using either IS-2000 or IS-856. To help manage the different availabilities of air interface protocols in different areas, a mobile node may be provisioned with a preferred roaming list (PRL) that identifies what systems and/or air interface protocols are preferred in different areas. For example, a PRL may specify that IS-856 is preferred over IS-2000 because of its higher potential data rate.
Nonetheless, certain situations can result in having a mobile node use a non-preferred protocol for communications, even though a preferred protocol is available. One such situation can occur as a result of handoffs that are made as a mobile node moves through different areas that have different protocol availabilities. For example, when a mobile node that is engaged in a communication session moves from an area in which only IS-2000 is available to an area in which both IS-856 and IS-2000 is available, the mobile node may continue using IS-2000 for the communication session, even though IS-856 is available and preferred.
Accordingly, there is a need to provide ways in which a mobile node can make better use of a preferred air interface protocol in areas where the preferred protocol is available.